Russian leader Vladimir Putin has warned the international community of “consequences” over any attempted interference as he ordered a military operation in Ukraine.

       Mr Putin announced what he termed a “special military operation”, triggering a perilous crisis in the heart of Europe. Ukraine’s envoy to the UN said Mr Putin had “declared war”, even as diplomats had gathered to try and find a solution.

       In a televised address at around 6am in Moscow, the Russian leader warned of the consequences over foreign interference in Russia’s actions. He claimed Russia did not intend to occupy Ukraine permanently and urged Ukrainian troops to put down their weapons.

       “Our plans are not to occupy Ukraine, we do not plan to impose ourselves on anyone,” he said.

       Yet, as he spoke, there were reports from Kiev of explosions close to the city, suggesting that the operation was already underway.

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       In Washington, US president Joe Biden warned that the US and its allies would respond in a “united and decisive way”, while at the United Nations, UN Secretary General Secretary-General António Guterres asked the Russian leader to withdraw his troops and “give peace a chance”.

       Joe Biden, who plans to address the American public on Thursday, said: “The world will hold Russia accountable.”

       The flurry of news early on Thursday morning in Europe appeared to suggest that the weeks of simmering tensions over the perceived threat to Ukraine from Russia has reached a new and fraught stage, with the potential for further escalation.

       It was not immediately clear how extensive the Russian operation was, and whether any Russian action would be focussed in the Donbass region of eastern Ukraine.

       In the early hours of Thursday, Ukraine’s leader had warned that his country would protect itself and that tens of thousands of people could die in the conflict.

       In an emotional address, President Volodymyr Zelensky insisted the people of Ukraine wanted peace.

       Yet, he said if Russia were to push ahead with an invasion, his country would defend itself.

       “The Ukrainian people want peace,” said Mr Zelensky. “The government in Ukraine wants peace and is doing everything it can to build it.”

       In a speech delivered in Russian and which was partly directed at Russia and its leadership, he added: “If we are attacked, if someone attempts to take away our land, our freedom, our lives, the lives of our children, we will defend ourselves.”

       He added: “When you attack us, you will see our faces, not our backs.”

       Mr Putin had accused the US and its allies of ignoring Russia’s demands to stop Ukraine from joining Nato and offer Moscow security guarantees.

       He said the Russian military operation aimed to ensure a “demilitarisation” of Ukraine.

       Addressing an emergency session of the UN Security Council, US Ambassador Linda Thomas-Greenfield said the US believed a “full-scale invasion” of Ukraine was imminent”.

       “Tonight, we’re seeing the Russians close airspace, move troops into Donbass and move forces into combat ready positions,” she said.

       “This is a perilous moment. And we are here for one reason and one reason only, to ask Russia to stop return to your borders. Send your troops and your tanks and your planes back to their barracks and hangers and send your diplomats to the negotiating table.”

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       CNN correspondents report explosions in Kiev

       Britain’s UN envoy Ambassador Barbara Woodward said a wholly unprovoked attack on Ukraine was unfolding.

       “For months, Russia has been holding a gun to Ukraine’s head. Now, President Putin’s finger is on the trigger,” she said.

       “A full-scale conflict in a country of 44 million people will bring immense suffering, casualties on both sides and devastating humanitarian consequences.”

       Later, Ms Thomas-Greenfield said: “This is a grave emergency. Unfortunately, while we’ve been meeting in the Security Council tonight It appears that President Putin has ordered that last step at the exact time, as we are gathered in the council, seeking peace.”

       Shortly afterwards, Ukraine’s envoy to the UN, Sergiy Kyslytsya, told his Russian counterpart, Vasily Nebenzya, to explain why his president had gone on television and announced war.

       Mr Kyslytsya, warned it was “too late” for de-escalation.

       “Because it’s too late, my dear colleagues, to speak about de-escalation, too late,” he said. “The Russian president declared war.”

       The Russian representative dismissed that war had been declared, but that Russia was launching simply a “special military operation”.

       “The root of today’s crisis around Ukraine is the actions of Ukraine itself, who for many years were sabotaging its obligations under the [Minsk agreement],” said Mr Nebenzya.

       He claimed that the Russian operation aimed to protect residents in the separatist pro-Moscow regions of eastern Ukraine, “who for eight years have been cowering from Ukraine’s shelling”.

       He claimed that “Ukrainian provocation against those in Donbas not only has not stopped but has intensified,” which prompted separatist leaders in the regions of Luhansk and Donetsk to request Russian assistance.

       Russia currently holds the presidency of the UN Security Council.

       Mr Nebenzya said “we aren’t being aggressive against the Ukrainian people but against the junta that is in power in Kiev”.

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       He then ordered the meeting closed.

       Additional reporting Associated Press